[SMPEG] synchronisation

Hi,

Is a video stream synchronized to sys time even if there is no audio in the
stream?
I think so, but on a slow machines, it seems not :
a 0:32s video-only stream took about 1m30s to finish on my AMD K2 300MHz
while another video with audio in the stream did finished at the expected
time.

Am I wrong or the video decoding thread synchronizes itself on the sound
thread? And if i am right, how can i force sys time synch on video only
streams?

thx

Alexis